Power semiconductor devices for high-voltage applications often use vertical double-diffused metal-oxide-semiconductor field effect transistors (VDMOSFETs) or laterally diffused metal-oxide-semiconductor field effect transistors (LDMOSFETs). In order to increase the breakdown voltage of high-voltage semiconductor devices, several methods are commonly in use, for example: the doping concentration of a deep well region (or known as drift region in the art) is reduced, the depth of the drift region is increased, or the length of an isolation structure (or known as field oxide layer in the art) underlying a gate is increased.
However, when the breakdown voltage of a power semiconductor device is increased by the above-described ways, the resistance in the ON state (ON-resistance) or the size of the transistor is increased as well, which undesirably reduces the performance of the device or increases the device area of a semiconductor device.
Thus, there exists a need in the art for development of a semiconductor device, capable of increasing the breakdown voltage while preventing the ON-resistance or device size from increasing.